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(11) | EP 0 062 400 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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Forming high-density carbon material by hot pressing Herstellung hochverdichteten Kohlenstoffmaterials durch Heisspressen Obtention de matériau carboné de haute densité par frittage sous pression |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to carbon material and, more particularly, to a method of forming shaped carbon material of high hardness and strength as set out in the introductory part of claim 7.
[0002] Shaped carbon material has hitherto been produced by loading a mass of carbon powder into a suitable receptacle. The loaded carbon mass is compacted under pressure at room temperature by producing a predetermined reduction in the volume of the receptacle followed by heating to make the powder coherent. A shaped block yielded from the preliminary treatment may then be subjected to a further compaction under simultaneous heating and pressure. The block is then cooled under pressure. Various attempts have been exercised to increase the density and improve the quality of the final carbon product, including choice of binder materials and removal of volatile components contained in the raw carbon material. These prior techniques have, however, proved to be either unsatisfactory or inefficient. Carbon materials produced by the prior art have left much to be desired as to their quality, especially, hardness and strength. Furthermore, even carbon materials of inferior hardness, density and other quality factors could hardly be produced and reproduced with consistency as to these factors and, let alone, with reliance and efficiency.
[0003] Accordingly, the present invention seeks to provide a new, efficient and reliable method of producing a shaped carbon material of high hardness, strength and density.
[0004] The present invention also seeks to provide a novel method which permits the continuous production of shaped carbon materials of uniform high hardness, strength, density, size and other quality factors.
[0005] Thus, the present invention is characterised in that the temperature and pressure are such as to produce liquefaction of a central region of the compressed body of graphite and sintering of the remainder thereof whereby upon the subsequent cooling of said body while under continuous pressure the solidified liquefied portion is surrounded by a sintered matrix.
[0006] These and other features of the present invention as well as advantages thereof will become more readily apparent from the following description made with reference to the accompanying drawings in which:
Fig. 1 is a sectional view in elevation diagrammatically illustrating an arrangement for practising the method of the invention in which pressure is applied to a cylindrical columnar carbon body retained in a conforming receptacle in opposite directions along the same axis;
Fig. 2 is a similar view illustrating another arrangement for forming a rectangular columnar carbon body according to the invention in which the receptacle is collapsible in two dimensions;
Fig. 3 is a cross sectional view taken along line III-III in Fig. 2; and
Fig. 4 is a sectional view in elevation diagrammatically illustrating another arrangement for the practice of the invention in which pressure is applied to a carbon body along X-, Y-and Z-axes which are orthogonal to one another.
[0007] Referring first to Fig. 1, a graphite-carbon body 1 is deposited in and firmly retained within a collapsible receptacle 2 which has its predetermined initial volume conforming to the initial mass of the body 1. The receptacle 2 is cylindrical and defined by the wall of a cylindrical bore 3a formed in a block 3 which may have cylindrical or rectangular outer walls 3b. A pair of punches 4 and 5 which are movable axially or along an X-axis are inserted in the cylindrical bore 3a one from each end, and are advanced slidably therein to define the initial volume of the receptacle 2 conforming to the size of the body 1. The body 1 may be a precompacted cylindrical block having a predetermined diameter. Preferably, a mass of fine grained graphite-carbon powder may be loaded in the receptacle 2 to constitute the initial carbon body 1 to eliminate the separate step of precompaction.
[0008] In the forming operation, the punches 4 and 5 in the bore 3a are axially advanced towards each other to compress the body 1 until a predetermined reduction of the volume of the receptacle 2 and hence of the body 1 is attained. The block 3 is constructed to be sufficiently rigid to maintain itself and the body 1 against lateral expansion. The initial pressure step is followed by simultaneous heating and pressure. It is essential that the body 1 is held under pressure exerted by the punches 4 and 5 and is heated to an elevated temperature for a period such that a central portion of the body 1 is liquefied as shown at 6. While the remainder thereof is sintered or becomes coherent substantially in the solid state. The pressure preferably ranges in excess of 50 tons/cm2 (0,5 - 106N/cmz and, more preferably, in excess of 100 tons/cm2 (1 . 106N/cmz). To protect the block 3, the wall 3a of the bore 3 or the body 1 may have a ceramic or like heat-resistant coating applied thereon. To assist the body 1 under simultaneous heating and axial pressure to resist lateral expansion, a heat-resistant ribbon wire coil 7 composed of carbon fiber is securely seated on the wall of the bore 3a, running spirally around the body 1.
[0009] Heating to cause a central portion of the body 1 under pressure to liquefy and the remainder thereof to sinter may be effected by passing a high-amperage electric current preferably directly through the body 1. To this end, an electrical power supply 8 is provided having _orte pole electrically connected to the upper punch 4 and the other pole electrically connected to the lower punch 5 to pass a resistive heating current between the punches 4 and 5 through the body 1. The punches 4 and 5 which serve as electrodes may be of a graphite-carbon material, preferably made according to the method of this invention. Likewise, the block 3 may be of a graphite-carbon material, preferably made according to the present method. The heating current may also be passed selectively through the block 3 to externally heat the body 1 or may be passed both through the body 1 and through the surrounding block 3.
[0010] Subsequent to the selective liquefaction of a center region 6, the body 1 is allowed to cool while held under pressure exerted by the punches 4 and 5 to solidify the liquefied region. It has been found that the central region 6 of the body 1 which is liquefied and solidified is substantially spherical in shape.
Example 1
[0011] A cylinder and punch arrangement as generally shown in Fig. 1 is used to form a cylindrical receptacle 2 having a diameter of 100 mm in which a mass of powdered graphite carbon of 100 mesh (150 µm) particle size is loaded to constitute the carbon body 1. The body is compressed between punches 4 and 5 under a pressure of 200 tons (2 . 106N). The body 1 held under pressure is heated by passing therethrough an electric current of a current density of 2500 amperes/cm2 for a time period of 40 minutes and subsequently is allowed to cool. It is found that the resulting body is extremely hard, having a central region once liquefield and then solidified in a spherical shape during the process, and has a density of 96% and a crushing strength of 750 kg/cm2 (73,5' N/mm2).
[0012] The receptacle 2 in the arrangement of Figs. 2 and 3 is rectangular for retaining a rectangular columnar precompacted or powdery mass of carbon material 1 therein and is defined by a pair of blocks 9 and 10 and another pair of blocks 11 and 12 as well as the punches 4 and 5. The blocks 9 and 10 have their body retaining surfaces 9a and 10a orthogonal to a Y-axis and the blocks 11 and 12 are inserted into the space defined by the surfaces 9a and 10a and driven axially slidably therewith to apply pressure from mutually opposite directions of the Z-axis orthogonal to the Y-axis, while the punches 4 and 5 are driven to apply pressure from opposite directions along the X-axis orthogonal to the Y- and Z-axes. Further pressure is applied externally to the blocks 9 and 10 in the opposite directions of the Y-axis to resist expansion in these fatter directions by the body compressed by the X-axis punches4. and 5 and the Z-axis blocks 11 and 12. With the body 1 held under two- or three-dimensional pressures, it may be heated again by a resistive heating current passed therethrough from the supply 8 to a sufficiently high temperature and for a sufficient time period to cause a center region 6 to be fully liquefied in a substantially spherical form and the remainder to be sintered. It is essential that the body 1 is cooled while continuously under pressure to form an improved carbon material.
[0013] Fig. 4 shows a further, preferred arrangement for pressurising in which each pair of blocks 4 and 5 (punches) (not shown); 9 and 10; 11 and 12 are driven in opposite directions to apply pressure along their own axes, X, Y, Z so that the body is compressed three-dimensionally. The receptacle 2 which is defined by these blocks is shown to be rectangular. In this arrangement, the side walls 9b, 10b of the blocks 9, 10 are arranged to slide on the surfaces 12a, 11 a of the blocks 12, 11, while the blocks 9 and 10 are driven towards each other across the body 1 along the Y-axis. Likewise, the side walls 11 b, 12b of the blocks 11, 12 are arranged to slide on the surfaces 9a, 10a while the blocks 11 and 12 are driven toward each other across the body 1 along the Z-axis. The upper and lower blocks or punches 4 and 5, though not shown in this Figure, are likewise arranged so that the volume of the receptacle 2 is reduced gradually as the blocks 4 and 5; 9 and 10; and 11 and 12 are driven simultaneously or successively from one pair to another or from one block to another. Here again, while under pressure, the body 1 is heated to an elevated temperature and for a period such as to form one or more liquefied regions 6 in a central zone of the body 1 and is then cooled to solidify these regions surrounded by a region which is simply sintered or made coherent in a solid state.
Example II
[0014] A press arrangement as generally shown in Figs. 2 and 3 is used to form a cubic carbon material 1 of 1 cm2 from a mass of powdered graphite carbon of a particle size of 100 mesh (150 µm).
[0015] A pressure of 200 tons (2 - 106N) is applied in two-dimensions to the mass while a resistive heating current is passed directly through the mass with a current density of 2500 amperes/cm2 for a time period of 40 minutes. It is found that the resulting body develops therein spherical regions solidified after liquefaction surrounded by a sintered matrix. The body is extremely hard and has a density of 98% at the theoretical density and a crushing strength (compressive strength) of 980 kg/cm2 (96,1 N/mm2).
Example III
[0016] Example II is followed using a mass which contains 10% by weight of petroleum pitch and the balance graphite carbon previously treated to remove volatile components therefrom. The mass is preliminary baked under a pressure of 2 tons (20 - 103N) and with heat delivered at 0.5 kilowatts/gram thereto. The preliminary baked body is pulverized to a powder of 100 pm to constitute the mass 1 of carbon material of Example II and is loaded into the arrangement of Fig. 4. The carbon product that results has a density of approximately 100% (theoretical density) and a crushing strength (compressive strength) of 1000 kg/cm2 (98,1 N/mm2).
1. A method of forming a shaped carbon material, comprising the steps of:
depositing graphite in a collapsible receptacle shaped and dimensioned to tightly retain said graphite therein, said receptacle being collapsible in at least one dimension under external pressure while holding the graphite against expansion;
applying a pressure externally of said receptacle to compress said graphite therein from the mutually opposite directions of at least one of three mutually orthogonal axes (X, Y and Z) to collapse and reduce the volume of the receptacle;
simultaneously compressing and heating the graphite; and
subsequent cooling the graphite while under continuous pressure, characterised in that the temperature and pressure are such as to produce liquefaction of a central region of the compressed body of graphite and sintering of the remainder thereof whereby upon the subsequent cooling of said body while under continuous pressure the solidified liquefied portion is surrounded by a sintered matrix.
2. A method according to Claim 1 characterised in that said receptacle is collapsible
in two dimensions.
3. A method according to Claim 1 characterised in that said receptacle is collapsible
in three dimensions.
4. A method according to Claim 1, 2 or 3 characterised in that graphite deposited
in the receptacle is in the form of a mass of powdered graphite carbon.
5. A method according to Claims 1, 2 or 3 characterised in that the graphite deposited
in the receptacle is in the form of precompacted graphite carbon.
6. A method according to Claim 4 or 5 characterised in that said body also contains
petroleum pitch.
7. A method according to any one of Claims 1 to 6 characterised in that said central
region is liquefied and solidified in a substantially spherical form.
8. A method according to any one of the preceding claims, further characterised by
the step of securely holding said graphite in a heat- resistance ribbon wire coil
of carbon fiber at least during said simultaneous heating and pressure.
9. A shaped carbon material produced by the method according to any preceding claim
characterised by a density of 96% to 100% (theoretical density) and a compressive
strength of 73,5-98,1 N/mm2 (750 kg/cm2 to 1000 kg/cm2).
10. A shaped carbon material when made according to the method of any one of Claims
1 to 8.
1. Verfahren zur Herstellung einer geformten Kohlenstoffmasse, bei dem Graphit in
einem verkleinerbaren Behälter in enger Anlage an die Behälterform eingebracht wird,
wobei der Behälter unter äußerem Druck in wenigstens einer Richtung verkleinerbar
ist und das Graphit gegen Expansion hält, und bei dem auf das Äußere des Behälters
zur Komprimierung des in ihm enthaltenen Graphits von entgegengesetzten Richtungen
wenigstens einer von drei Orthogonalachsen (X, Y, Z) Druck angewandt wird, um den
Behälter zu verkleinern und das Volumen des Behälters zu reduzieren, und bei dem gleichzeitig
der Graphit komprimiert und erhitzt wird und anschließend der Graphit unter fortgesetztem
Druck gekühlt wird, dadurch gekennzeichnet, daß die Temperatur und der Druck so gewählt
werden, daß ein zentraler Bereich des komprimierten Graphit- Körpers verflüssigt und
der übrige Teil des Graphit-Körpers gesintert wird, wodurch bei an schließendem Abkühlen
des Körpers unter kontinuierlichem Druck der verfestigte, verflüssigte Teil von einer
gesinterten Matrix umgeben ist.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Behälter in zwei Dimensionen
verkleinerbar ist.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Behälter in drei Dimensionen
verkleinerbar ist.
4. Verfahren nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß der in den Behälter
eingebrachte Graphit eine Masse aus gepulvertem Graphit-Kohlenstoff ist.
5. Verfahren nach Anspruch 1, 2, oder 3, dadurch gekennzeichnet daß der in den Behälter
eingebrachte Graphit vorverdichteter Graphit-Kohlenstoff ist.
6. Verfahren nach Anspruch 4 oder 5, dadurch gekennzeichnet, daß der Graphitkörper
zusätzlich Petroleumpech enthält.
7. Verfahren nach einem der Ansprüche 1-6, dadurch gekennzeichnet, daß der zentrale
Bereich in einer im wesentlichen kugeligen Form verflüssigt und verfestigt wird.
8. Verfahren nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, daß der
Graphit in einer hitzebeständigen Banddrahtspule aus Kohlefaser wenigstens während
der gleichzeitigen Anwendung von Druck und Wärme festgehalten wird.
9. Geformte Kohlenstoffmasse hergestellt nach dem Verfahren gemäß einem der vorstehenden
Ansprüche, gekennzeichnet durch eine Dichte von 96%-100% (theoretische Dichte) und
eine Druckfestigkeit von 73,5-98,1 N/mm2 (750 kg/cm2 bis 1000 kg/cm2).
10. Geformte Kohlenstoffmasse, hergestellt nach einem der Ansprüche 1-8.
1. Procédé de d'un matériau en carbone façonné comprenant les étapes consistant à
déposer du graphite dans un réceptacle rétractable conformé et dimensionné de manière
à retenir fermement le graphite à l'intérieur, ce réceptacle étant rétractable dans
au moins une dimension, sous l'effet d'une pression. extérieure, tout en maintenant
le graphite à l'encontre de toute extension; à appliquer une pression à l'extérieur
de ce réceptacle afin de comprimer le graphite s'y trouvant à partir de deux directions
opposées mutuellement suivant l'un au moins de trois axes (X, Y et Z) perpendiculaires
entre eux, afin de rétracter et réduire le volume du réceptacle; à chauffer et à comprimer
simultanément le graphite et à refroidir ensuite le graphite tout en maintenant une
pression continue, caractérisé en ce que la température et la pression sont choisies
de manière à produire la liquéfaction d'une zone centrale du corps comprimé en graphite
et le frittage du reste de ce corps si bien que lors du refroidissement subséquent
de ce corps sous une pression continue la partie liquéfiée et solidifiée se trouve
entourée par une matrice frittée.
2. Procédé suivant la revendication 1 caractérisé en ce que le réceptacle est rétractable
suivant deux dimensions.
3. Procédé suivant la revendication 1 caractérisé en ce que le réceptacle est rétractable
suivant trois dimensions.
4. Procédé suivant l'une quelconque des revendications 1 à 3 caractérisé en ce que
le graphite dans le réceptacle est constitué par une masse de graphite pulvérulent.
5. Procédé suivant l'une quelconque des revendications 1 à 3, caractérisé en ce que
le graphite dans le réceptacle est constitué par du graphite précompacté.
6. Procédé suivant l'une quelconque des revendications 4 et 5 caractérisé en ce que
le graphite contient également du brai de pétrole.
7. Procédé suivant l'une quelconque des revendications 1 à 6 caractérisé en ce que
la zone centrale est liquéfiée et solidifiée sous une forme sensiblement sphérique.
8. Procédé suivant l'une quelconque des revendications précédentes caractérisé en
ce qu'il comprend en outre l'étape consistant à maintenir fermement le graphite dans
une bobine de fil ruban résistant à la chaleur, en fibre de carbone, au moins durant
le chauffage et le pressage simultanée.
9. Un matériau en carbone façonné produit par le procédé suivant l'une quelconque
des revendications précédentes caractérisé en ce qu'il a une densité allant de 96%
à 100% et une résistance à l'écrasement allant de 73,5 à 98,1 N/mm2.
10. Un matériau en carbone façonné fabriqué par le procédé suivant l'une quelconque
des revendications 1 à 8.